Meld helps you compare files, directories, and version controlled projects. It provides two- and three-way comparison of both files and directories, and has support for many popular version control systems. Meld helps you review code changes and understand patches.
https://meldmerge.org/
It's in the Debuntu repos and there's a Windows and unofficial Mac version too. It's infinitely better than trying to use diff to see what's changed between two or three files.
VERY handy tool!